The present invention relates to a method for evaluating a structural strength of cancellous bone, which is required during the insertion of an implant within bone or during diagnosis of osteoporosis; and more particularly, to a method for evaluating a structural strength of cancellous bone using a simple X-ray image and a computer readable media incorporating a program for implementing the method therein.
The surface of bone is covered with a periosteum and the bone contains a dense cortical bone positioning in the proximity of the surface and a cancellous bone positioning in the proximity of a bone marrow. The component ratio of the cortical bone and the cancellous bone is dependent on a region in body and the osteoporosis lads to a simultaneous reduction of the cortical and cancellous bone mineral contents. In normal person, a creation and absorption of bone are in balance and thus the total bone mineral content is preserved. However, an aged person with a degraded bone creation function or a postmenopausal woman whose an estrogen secretion is degraded to result in an increased bone absorption function may be extremely vulnerable to the osteoporosis. In recent years, osteoporotic patients in young men and women are considerably increasing due to underexercise or drug reactions. Generally, osteoporosis makes weak a structure of bone, thus invoking a fracture of spine, femur, radius and so forth, and leading to death in some fracture cases.
The reduction of the bone mineral content may be an obstacle to the success of a fracture treatment or a dental implant operation. Especially, in a dental implant operation, a bone structure where the implant is inserted should be mechanically stable so that the inserted implant is strongly fixed to the bone. The structural strength of the bone may be mainly determined by the cortical bone. However, the cancellous bone also plays an important part during the insertion of the implant within the bone. A weak cancellous bone prevents a root portion of the implant inserted within the bone from being strongly fixed to the cancellous bone, leading to a degraded bearing capacity of the implant. Accordingly, what is needed is a method for evaluating the structural strength of the cancellous bone to determine the possibility of the surgical or dental implant operation.
Conventional methods, which estimate the structural strength of the cancellous bone using an x-ray image, include a bone trabecular pattern analysis technique, a Fourier transform technique and a Fractal dimension technique.
First, the bone trabecular pattern analysis technique is a way, which examines a projection pattern of a cancellous bone presented on a simple x-ray image, to thereby determine the structural strength of cancellous bone. Although such technique is being widely used during the surgical operation, the dental implant operation and the osteoporosis diagnosis, it suffers some drawbacks that it causes a significant inter-operator variations and that a change in acquisition condition for the x-ray image significantly lowers the reproducibility by the same operator.
The Fourier transform technique is a way, which performs the Fourier transform on a bone trabecular image and analyzes Fourier components in the frequency domain, to thereby measure an orientation or density of the bone trabecular pattern. However, this technique is not effective except when a bone trabecular image does not contain any soft-tissue effect. In practice, when a thick soft tissue is overlapped as in the femoral neck, the x-ray image is extremely degraded, which, in turn, leads a sharp decrease in effectiveness of the Fourier transform technique.
The fractal dimension technique is a way, which computes a fractal dimension in the bone trabecular image to measure a structural strength of cancellous bone. Some investigations have provided a result that the cancellous bone with a high fractal dimension is more resistive against external force. However, such a result is not decisive yet.
Instead of using the x-ray image, there is a technique that utilizes a quantitative computed tomography (QCT) for measuring the structural strength of the cancellous bone. The QCT technique allows simultaneous measurements of volume and structure of the cancellous bone. Since the QCT technique provides three-dimensional bone density information, it has the ability to separately measure an actual structure and density of the cortical and cancellous bones. This is the most outstanding feature of the OCT technique and this feature can be used to measure the structural strength of the cancellous bone. However, the QCT technique suffers from a drawback that the QCT equipment is highly expensive.
In addition to the afore-mentioned methods, studies for analyzing a bone trabecular pattern presented on the x-ray image are actively in progress. The reason is that since most hospitals are equipped with an x-ray imaging system, it is not necessary to equip an additional instrument for the analysis of a bone trabecular pattern, and a digital x-ray sensor such as a charge-coupled device (CCD) is introduced to enhance a resolution and quality of image, allowing the analysis of the bone trabecular pattern with ease. Nevertheless, clinically available technique to analyze a trabecular pattern is not well developed yet. Generally, analysis of a trabecular pattern should take into account both structure and density aspects of the trabecular pattern. However, conventional methods fail to take into account both structure and density aspects of a trabecular pattern.
It is, therefore, an object of the present invention to provide a method for analyzing a bone trabecular pattern presented on an x-ray image, to thereby evaluate a structural strength of cancellous bone.
It is another object of the present invention to provide a computer readable media incorporating a program for implementing the method therein.
In accordance with one aspect of the present invention, there is provided a method for evaluating a structural strength of cancellous bone, comprising the following steps of acquiring an x-ray image and defining a region of interest on the acquired x-ray image; extracting a bone trabecular pattern in the defined region of interest; and setting an index of the structural strength of the cancellous bone using an area density obtained from the extracted bone trabecular pattern.
In accordance with another aspect of the present invention, there is provided a computer readable media incorporating therein a program for implementing the following functions of acquiring an x-ray image and defining a region of interest on the acquired x-ray image; extracting a bone trabecular pattern in the defined region of interest; and setting an index of the structural strength of the cancellous bone using an area density obtained from the extracted bone trabecular pattern.